ments of 10 ml. until a spot test with potassium ferricyanide indicates the presence of an excess. Add 15 ml. of a freshly prepared 15% solution of ammonium peroxydisulfate and swirl the contents of the flask for 1 minute. Titrate slowly with a 0.03N solution of potassium permanganate to a definite pink end point which is stable for a t least 1 minute. It is preferable to standardize the permanganate solution against a solution of pure vanadium metal of known concentration. Transfer an aliquot of the first effluent solution containing not more than 80 mg. of molybdenum to a 400-ml. beaker, add 10 ml. of nitric acid and 20 ml. of sulfuric acid (1 I), and evaporate to dense fumes of sulfur trioxide. Add nitric acid drop by drop as needed to destroy the organic matter (citric acid,, dilute t o 200 ml.
+
with water, and determine the molybdenum by the gravimetric benzoin oxime procedure of Knowles (3). Transfer a 250-ml. aliquot of the first effluent to a 600-ml. beaker and evaporate to about 200 ml. During the evaporation, add a few ml. of nitric acid as necessary to oxidize the molybdenum to the colorless state. Determine the phosphorus content of this solution via two precipitations as magnesium ammonium phosphate and subsequent ignition to magnesium pyrophosphate. RESULTS
The procedure as described affords a clean and complete separation of vanadium from molybdenum and phosphorus, without loss of any of the constituents to the exchange column.
Checks on duplicate samples are as good as can be obtained on analysis of pure solutions of the elements taken individually. The accuracy of the method has been checked by analyses of synthetic mixtures in various proportions, and is illustrated in Table I. LITERATURE CITED
(1) Ablov, A. V., Malinovskii, T. I., Dedyu, V. I., Zh. Neorgan. Khim., 4,
397 (1959). (2) Klement, Robert, Z.Anal. Chem., 136, 17 ~- 11952). (3) Knowles, H. B., J. Res. ATutl. Bur. Std. 9, 1 (1932).
WILLIAM H. PRICE ROBERT H. MAURER Climax hlolybdenum Co. of Michigan Detroit, Mich.
A Modified Conway Method for Determining Ammonia in Uranium Compounds SIR: The determination of ammonia in ammonia-containing compounds is usually carried out by distillation of the strongly alkaline solution absorbing the ammonia expelled in an excess of standard acid and back-titration of the latter with standard base. This method will fail, however, if the compound also contains other components that evolve ammonia as they decompose on heating. In our case, the ammonia uranium compounds t o be analyzed (in literature usually referred to as “.4DU”) may also contain urea uranate or urea. Heating solutions of these compounds induce3 the liberation of ammonia by hydrolysis, thus leading t o an erroneous ammonia content of the samples. An alternative method for the determination of ammonia, the microdiffusion method of C o n m y (1, 2 ) , is well known to biochemists and clinicians although it has found little application in inorganic chemistry. In this method the entire determination is carried out a t room temperature. Hence, urea hydrolysis is now avoided. Furthermore, the Conway method has some distinct advantages over the macrodistillation method: the samples required are small, the apparatus is simple, and the method is suitable for a large series of determinations. This method does, however, require a longer time of analysis. We modified the method t o suit our work on ammonia-containing uranium oxide hydrates and we think that it may have much wider applications. I n view of this, procedures for the determination of nitrate and carbon dioxide are also being developed. 596
ANALYTICAL CHEMISTRY
Figure 1. paratus
Standard absorption ap-
Material: borosilicate glass.
Units: rnm.
EXPERIMENTAL
Apparatus. The diffusion apparatus consists of a small thick-walled dish with a concentric inner compartment of lower height (Figure 1). The apparatus can be closed with a flat glass plate and leaks are prevented by greasing the outer rim. The Conway dish is commercially available. Reagents. Potassium carbonate, saturated solution in contact with solid potassium carbonate: Dissolve 560 grams in 500 ml. of distilled water. Mixed indicator, methyl red-bromcresol green: Dissolve 0.5 gram of methyl red and 0.75 gram of bromcresol green in 1000 ml. of 96% ethyl alcohol. Sealent paste. Mix in a mortar distilled water (300 ml,), glycerol (150 ml.), and saturated potassium carbonate solution (50 ml.). .4dd 35 grams of high viscosity carboxymethyl cellulose with continuous mixing. Finally, add 10 ml. of Teepol (trade name for Shell detergent, sodium salt of secondary alkyl sulfates) and allow the mixture to stand for a t least 24 hours. The paste may be stored indefinitely.
Procedure. A sample, containing up to 0.2 to 0.3 meq. of ammonia, is weighed into the outer compartment of the absorption apparatus. This sample is dissolved in approximately 1.5 ml. of IN-hydrochloric acid, while care is taken t h a t no droplets of acid enter the inner compartment. Into the inner compartment 1 ml. of standardized 0.4W sulfuric acid is measured from a microburet. The outer rim of the vessel is then greased with the sealent paste. To expel the ammonia from the sample solution the liquid must be made strongly alkaline with potassium carbonate solution. However, a t this point, addition of carbonate to the acid liquid might cause splashing due to the evolution of carbon dioxide. Therefore, the pH in the outer compartment is first raised with some 1N sodium hydroxide. On the addition of each drop a slight precipitate is formed that dissolves on swirling the dish. The addition is stopped when the precipitate tends to remain. The addition of too much sodium hydroxide would cause loss of ammonia. Finally, 1 ml. of saturated potassium carbonate solution is added quickly to the outer compartment and the vessel is closed immediately. The closed apparatus is now swirled carefully to make sure that the solutions in the outer compartment are homogeneously mixed. After standing a t room temperature for at least 4 hours (but preferably for one night), the liquid in the inner compartment is back-titrated with standardized 0.lN sodium hydroxide, methyl red-bromcresol green being used as an indicator. DISCUSSION AND RESULTS
In the determination of ammonia in uranium compounds we preferred to expel as much ammonia as possible
from the sample while the latter was in solution. This was done by the addition of carbonate as a complexing agent for the uranyl ion at high pH. After several hours a slight, slow precipitation was noted but this did not appreciably influence the result. In the original method the ammonia expelled was absorbed in a boric acid solution, in which the ammonia was titrated with standard acid. Our results with boric acid as absorbing medium were rather poor. We therefore substituted standard sulfuric acid for boric acid and back titrated the excess of sulfuric acid with standard base. The method was tested with standard ammonium compounds in the presence of iiranium and nitrate ions. For the
conditions indicated above the accuracy of the method is well within 1%. This accuracy might be further increased by applying the special microequipment described by Conway. However, the procedure is quite satisfactory in such cases as ours, where only a few per cent of ammonia are normally present. The influence of waiting time for diffusion was studied. Whereas 4 hours are generally sufficient for complete absorption, we prefer to prepare a series of analyses one day and backtitrate them the next. If preferred, the time of diffusion can be shortened by increasing the reaction temperature to about30’ C. It is essential t o keep the volume in the outer chamber as small as possible
to promote the rate of diffusion of the ammonia. LITERATURE CITED
( 1 ) Conway, E. J., “Micro-diffusion Analysis and Volumetric Error,” Crosby Lockwood & Son Ltd., London, 1962. ( 2 ) Conway, E. J., Byrne, A., Biochem. J. 27,419 (1933). C. J. G. A L T M A N N ~
B. H. J. DE H E E R ~ M. E. A. HERMANS
Reactor Development Group N. V. KEMA Arnhem, Netherlands 1 Present address: Central Laboratory Staatsmijnen, Geleen, Netherlands. 2 Present address: Chemistry Depare ment, University of Sijmegen, Xetherlands.
Some Experimental Parameters of the Beckman Model KF-3 Aquameter SIR: A recent article by Burns and Rluraca ( 2 ) discussed some experimental parameters associated with the Beckman KF-2 ilquameter. In the past 2 years we have carried out some 4000 individual titrations of m-ater in organic solvents with a Beckman Model KF-3 Aquameter using the Karl Fischer Reagent (KFR) as the titrant, and we feel that the data obtained will readily supplement the KF-2 work. The Model KF-2 Aquameter utilizes a circuit n-herein the platinum electrodes are one arm of a n impedance bridge and three-stage amplification is used to detect a modified dead-stop endpoint. The solution being titrated must have sufficient conductance for this bridge to perform successfully; therefore, the instrument is recommended only for methanol solutions. The Model KF-3 Aquameter (3, 4 ) on the other hand, utilizes the straightforward dead-stop endpoint detection cystem with neither transistor nor vacuum tube amplification, but uses a Ielay system for the same purpose (4). An adjustable polarizing voltage from a transformer-rectifier unit porrered from the line voltage is connected to tmo platinum electrodes in series with the coil of a sensitive relay, requiring from 15 to 30 pa. to close, and is equipped nith a variable shunt to permit adjustment of its sensitivity. The contacts of this delicate relay cannot handle much power and are therefore connected in wries with the coil of a more powerful relay and a supply voltage. This is, in effect, amplification by relay. .4t the endpoint (a current greater than 30 pa.) this relay shuts off the buret solenoid and starts the timing device described earlier ( 2 ) . The Model KF-3, because of the small current flow required, is not
limited to methanol solutions, but may be used for both miscible and immiscible samples in many solvents without the aid of a pretitrated methanol solvent. Although most of our work centered upon the water content of chloroform, 1-decanol, and nitrobenzene. we successfully analyzed samples of pyridine, benzene, amylene, 2,2,4-trimethyl pentane, methyl-phenyl ketone, methylhexyl ketone, iso-amyl alcohol, acetone, and acetonitrile. The concentration range of the samples was from 50 mg. of water per nil. of solution to 0.20 mg. of water per ml. of solution. A feed rate of 7.5 ml. of Karl Fischer Reagent per minute was used. Using 10-ml. burets for both the Karl Fischer Reagent and the standard water-methanol (WM) solution, the final volume of the solution at the endpoint was approximately 19 ml. The neutralized reaction mixture was removed from the vessel after each titration via a siphon tube. The timer was set at the 30-second position. A small modification mas made in the Aquameter to facilitate rapid change over from the forward to the back titration procedure and vice versa. For the forward titration, the electrodes are connected into the high side of the dual range microrelay circuit, so that the power relay will be activated when the current increases above 30 pa. For the back titration, the electrodes are connected into the low side of the microrelay circuit, so that the power
Solvent Chloroform 1-Decanol Methanol Nitrobenzene
relay will be activated when the current decreases below 30 pa. Usually, this means completely dismantling the KF-3 Aquameter t o change the leads from the high to the low poles on the microrelay. A single pole double throm switch was mounted on the back of the chassis to avoid time consuming dismantling. Thus, a change in the position of the switch and the rapid interchange of burets enables the conversion to be carried out in a matter of a few minutes. d comparison of the reproducibility of the forward titration (Karl Fischer Reagent as titrant) and the back titration (a standard n-ater-methanol solution) was carried out. For the forward titration, the KFR/WYI ratio mas 0.983 1 0.012 and the KFR,’Rh!I for a different set of solutions n-as 1.356 ik 0.043 by the back titration procedure. The reproducibility of forward titrations of the water content of four organic solvents is shown in Table I. Burns and Rluraca (2) found that certain salts catalyzed the reaction of the Karl Fischer Reagent xhile titrating the Tvater in solid samples. Blomgren and Jenner ( 1 ) described the addition of pyridinium iodide as a stahilizer to slow down the reduction rate of the titer of the Karl Fischer Reagent. We found that addition of 80 gram? of anhydrous pyridinium iodide per liter of Karl Fischer Reagent appeared t o be the optimum concentration to stabilize the solution.
Table 1. Reproducibility Data Dielectric Sample, Titration No. of HnO Standard constant ml. time samples found, yo deviation 10.0003 2min. 20 0.0434 5 25.00 6.5 33 35
5.00 10.00 10.00
1.5min. 3 min. 2 min.
20 20
20
0.2985 0.2895 0.1428
10.0044 10.0029 10.0019
VOL. 35, NO. 4, APRIL 1963
597
